The overall goal is to synthesize experimental data at the membrane and molecular level into predictive mathematical models of the kidney that are useful in understanding both its normal and diseased function. The general purpose of the proposed research is to develop for the first time a mathematical and computer model that includes a realistic architecture, cellular and paracellular transport of water and solutes, and exchange of solutes and water between plasma and red blood cells. The development builds on simpler models, but requires the parallel processing capabilities of supercomputers.